Impact property modification of thermoplastic polymers by a variety of rubbers, elastomers, and rubbers combined with thermoplastics has been known for many years. Extensive interest has been shown for at least 30 years in rubbers combined with thermoplastics in a core-shell structure, typically prepared by emulsion polymerization, as exemplified by such commercial combinations as acrylate-butadiene-styrene (ABS) or methacrylate-butadiene-styrene (MBS) impact-property modifiers for poly(vinyl chloride), acrylic/methacrylic core-shell modifiers for polycarbonate, and the like.
In the case of the amide polymers collectively known as nylons, such as nylon 6 (polycaprolactam), nylon 66 (poly(hexamethylene adipamide)), and the like, impact strength may be improved by reacting an acid or anhydride functionality on the impact-property modifier with an amine group available on the polyamide. Such functionalized modifiers include ethylene/acrylic acid copolymers (British Patent No. 998,439), metal-ion neutralized ethylene/unsaturated acid copolymers (Murch, U.S. Pat. No. 3,845,163), acrylic rubber//methyl methacrylate-co-unsaturated acid core-shell polymers as taught in Owens and Clovis, U.S. Pat. Nos. 3,668,274, 3,796,771, 3,984,497, 4,086,300 and 4,148,846. Baer (U.S. Pat. No. 4,584,344) teaches modification with a core-shell polymer consisting of a crosslinked elastomer of particle size above 300 nanometers, with a shell containing a polymer of unsaturated carboxylic acid, styrene, and optionally a lower alkyl methacrylate and/or (meth)acrylonitrile. Impact-property modifiers which adhere to nylon, of particle size 0.01 to 3 micrometers (um) and of a tensile modulus 7-138,000 kilopascals (kPa) are disclosed in Epstein, U.S. Pat. No. 4,174,358, and similar modifiers are taught in German Offenlegungschrift 3,403,576. Polyamide-toughening reactive crosslinked acrylic rubbers having an outer layer of an alkyl acrylate and a polyamide reactive graft-linking monomer are disclosed in Novak, U.S. Pat. No. 4,474,927. Blends of nylon 6 and nylon 66 toughened with an ionic copolymer of an alpha-olefin with an unsaturated carboxylic acid, the acid moeity of which is at least partially neutralized with metal basic salts, are disclosed in Roura, U.S. Pat. No. 4,478,978. Such co-reacted modifiers may also improve the processing of the nylon, allowing melt strength sufficient for blow-molding, thermoforming, and the like. The modifiers of Owens and Clovis, above, are particularly related to the present invention.
General problems with incorporating impact-property modifiers into thermoplastic polymers have been (1) the difficulty of obtaining uniform dispersion of the modifier throughout the matrix polymer and (2) breaking down aggregates of the modifier to a dispersed domain within the matrix polymer having optimum size for best impact resistance, surface appearance, gloss development, absence of voids, and the like. These problems exist even when the modifier particles are quite small, as when they are made in emulsion, because the processes of isolation from emulsion and incorporation into the matrix polymer cause the particles to aggregate, and they may not be readily dispersed. Such dispersion problems are exemplified in Dunkelberger, U.S. Pat. No. 4,167,405, in which a pre-dispersion of impact-property modifier in a higher viscosity nylon is required to obtain adequate dispersion of the modifier in low molecular weight nylon.
Dunkelberger (U.S. Pat. No. 4,440,905) teaches a class of polymers effective as dispersion aids for impact-property modifiers in poly(vinyl chloride), but does not teach or suggest the compositions of the present invention, nor suggest that his technology may be used to modify nylon. Grigo, U.S. Pat. No. 4,423,186, discloses copolymers of ethylene with (meth)acrylic acid combined with crosslinked butadiene rubbers for improved low-temperature resistance. Albee et. al., U.S. Pat. No. 4,412,040, disclose that neutralized, low-molecular-weight copolymers of ethylene/unsaturated carboxylic acids act as lubricants and dispersing aids in nylon, helping disperse finely divided, dispersible, inert material. This dispersing ability as applied to nylon is not taught.
Japanese Kokai 60/60,158 discloses copolymers of aromatic vinyl monomers with unsaturated carboxylic acids microdispersed in nylon to improve mechanical properties.
Impact-property modifiers which adhere to polyesters and polycarbonates, such as zinc-neutralized ethylene/acrylate/acrylic acid terpolymers, having particle sizes from 0.01 to 3 um and tensile modulus from 7 to 138,000 kPa, are disclosed in Epstein, U.S. Pat. No. 4,172,859.
European Patent Application No. 168,652 (Campbell and Conroy) teaches improved impact-strength resistance for polyphenylene oxide when it is blended with elastomers containing highly polar groups, such as sulfonated polyethylene.
Impact-property modifiers isolated from emulsions by spray-drying or coagulation often are difficult to maintain as free-flowing powders, especially if the modifier is a core-shell polymer with high elastomer content. Several solutions to the problems of sticking to equipment walls, ready compression of the modifier under load, and poor flow in air-veying systems are taught in the literature. Ferry et al. teaches inorganic flow aids and poly(methyl methacrylate) for acrylic- and butadiene-based impact-property modifiers (U.S. Pat. Nos. 3,985,703 and 3,985,794). Grandzol et al. teaches coagulating poly(methyl methacrylate) onto a MBS modifier (U.S. Pat. No. 4,463,131). Neither teaches or suggests the additive of the present invention.
An object of the present invention is to obtain a balance of surface appearance, impact strength and tensile strength in nylon and other thermoplastic polymers which is superior to the balance obtainable with conventional impact modifiers. Another object of the invention is to improve the processing behavior of the impact-property modifiers/polymeric additive combinations with thermoplastic polymer matrices, including those with which the modifiers do and do not react. Other objects will be apparent from the following discussion of the invention.